US9112379B2 - Pairing of components in a direct current distributed power generation system - Google Patents

Abstract

A method of signaling between a photovoltaic module and an inverter module. The inverter module is connected to the photovoltaic module. In an initial mode of operation an initial code is modulated thereby producing an initial signal. The initial signal is transmitted from the inverter module to the photovoltaic module. The initial signal is received by the photovoltaic module. The operating mode is then changed to a normal mode of power conversion, and during the normal mode of operation a control signal is transmitted from the inverter to the photovoltaic module. A control code is demodulated and received from the control signal. The control code is compared with the initial code producing a comparison. The control command of the control signal is validated as a valid control command from the inverter module with the control command only acted upon when the comparison is a positive comparison.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part of pending U.S. patent application Ser. No. 12/329,525 filed on Dec. 5, 2008, which claims priority to U.S. provisional patent application No. 60/992,589 filed Dec. 5, 2007. U.S. patent application Ser. No. 12/329,525 is also a continuation-in-part of U.S. patent application Ser. No. 11/950,271 filed Dec. 4, 2007, which claims priority to U.S. provisional patent application No. 60/916,815 filed May 9, 2007, U.S. provisional patent application No. 60/908,095 filed Mar. 26, 2007, U.S. provisional patent application No. 60/868,962 filed Dec. 7, 2006, U.S. provisional patent application No. 60/868,851 filed Dec. 6, 2006, and U.S. provisional patent application No. 60/868,893 filed Dec. 6, 2006. The present application is also a continuation-in-part of pending U.S. patent application Ser. No. 12/788,066 filed on May 26, 2010, which claims priority to U.S. provisional patent application No. 61/180,940 filed May 26, 2009.

FIELD AND BACKGROUND

1. Field

The present invention relates to power generation systems, and specifically to a system and method for reducing crosstalk while signaling between the components in direct current distributed power generation systems.

2. Related Art

A photovoltaic power generation system may incorporate one or more photovoltaic panels with optional electronic modules attached thereto. An inverter connects to the photovoltaic panels or electronic modules. Power output from the photovoltaic panels or electronic modules is direct current (DC) power. The electronic modules may perform direct current DC-to-DC conversion. The inverter inverts the DC power output to alternating current (AC) power.

As previously disclosed by the present inventors in US patent application publication 2008/0147335, the DC power cables connecting inverters to photovoltaic panels and/or electronic modules may provide a communication channel between the inverters and the photovoltaic panels or modules. The communication channel between inverters and modules, allows monitoring of the performance of the modules for monitoring temperature, current, voltage and power output of a the photovoltaic modules and potential allows for control of the modules.

Typically, lengths of cables connecting the inverter to the panels or modules may be long and may contain one or several wire cores. Within a photovoltaic installation, a wire at positive potential and a wire at negative potential electrically associated therewith may be physically proximate thereto only at a point of connection to a piece of equipment. However, elsewhere in the photovoltaic field, the wires may be separated and not be within the same cable run. The topography of the distributed power generation system to a large extent dictates the installation and placement of cable runs. Physical proximity of wires not having an electrical association may increase the chances of the wires in the cables being subject to the effects of noise if those wires are to be considered for signaling by DC power line communications. Crosstalk is a type of noise which refers to any phenomenon by which a signal transmitted on a cable, circuit or channel of a transmission system creates an undesired effect in another cable, circuit or channel. Crosstalk is usually caused by undesired capacitive, inductive, or conductive coupling from one cable, circuit or channel, to another. Crosstalk may also corrupt the data being transmitted. Typical known methods of preventing the undesirable effects of crosstalk may be to utilize the shielding of cables, modules, panels, inverters or using twisted pair cables. Additionally, filtering techniques such as matched filters, de-coupling capacitors or chokes may be used to prevent the undesirable effects of crosstalk. However, these typical ways of preventing the undesirable effects of crosstalk are typically unavailable or impractical for power line communications over DC lines in a power generation system and/or may be prohibitively expensive in terms of additional materials and/or components required.

In a photovoltaic power generation system, with power line communication over DC cables, it may be desirable to send a control signal between and an inverter and a particular photovoltaic module but no other modules. Crosstalk may cause the other photovoltaic modules in the power generation system to inadvertently receive the control signal which is of course undesirable.

Thus there is a need for and it would be advantageous to have a system and method of reducing cross-talk in DC power line communications in a distributed DC power generation system, e.g photovoltaic DC power generation system.

The term “memory” as used herein refers to one or more of read only memory (PROM), erasable programmable read only memory (EPROM), electrically erasable programmable read only memory (EEPROM), FLASH memory, optical memory, e.g. compact disk, switches, random access memory (RAM), magnetic memory such as a hard disk or other memory types known in the art.

The term “direct current (DC) power source” as used herein refers to (DC) power source such as batteries, DC motor generator; switch mode power supply (SMPS), photovoltaic panels and/or photovoltaic panels operatively attached to a converter module such as a DC to DC converter.

The term “photovoltaic source” as used herein refers to a photovoltaic panel and/or a photovoltaic panel operatively attached to a electronic module which includes for instance a DC-to-DC converter. The term “electronic module” and “photovoltaic module” are used herein interchangeably and refer to a functional electronic circuit attached to a photovoltaic panel.

The term “noise” as used herein in a communication channel, includes any unwanted signal finding itself in the communication channel. Sources of noise may include radio frequency interference (RFI), mains electricity hum, unsuppressed switching voltages and crosstalk.

The term “crosstalk” as used herein refers to any phenomenon by which a signal transmitted on a cable, circuit or channel of a transmission system creates an undesired effect in another cable, circuit or channel. Crosstalk is usually caused by undesired capacitive, inductive, or conductive coupling from one cable, a circuit, part of a circuit, or channel, to another.

The term “telemetry” as used herein refers to measurement, transmission and reception of data by wire, radio, or other means from remote sources. In the context of the present invention, telemetries are from the photovoltaic panels.

The term “transducer” as used herein refers to a device used for the conversion of one type of energy to another, for example, the device changes electrical energy in to electromagnetic energy and vice versa. The term “transducer” herein may also have functions of a sensor or detector. The terms “sensor” and “transducer” as used herein are used interchangeably.

The terms “signal”, “signaling” or “signaling mechanism” as used herein refers to a signal modulated on a carrier signal. The carrier signal may be an electrical or an electromagnetic signal. The signal may be a simple on/off signal or a complex signal which imparts information as data. For a modulated signal, the modulation method may be by any such method known in the art, by way of example, frequency modulation (FM) transmission, amplitude modulation (AM), FSK (frequency shift keying) modulation, PSK (phase shift keying) modulation, various QAM (quadrature amplitude modulation) constellations, or any other method of modulation. Although strictly, the terms “modulation” and “coding” are not equivalent, the term modulation and demodulation are typically used herein to include coding and decoding respectively.

The term “signal strength” as used herein refers to the magnitude of the electric field/current or voltage at a reference point that is a significant distance from a transmitting source. Typically, “signal strength” is expressed in voltage per length or signal power received by a reference point expressed in decibel (dB) per length (meter), dB-millivolts per meter (dBmV/m), and dB-microvolts per meter (dBμV/m) or in decibels above a reference level of one milliwatt (dBm).

The term “positive comparison” in reference to the comparison of two codes or two signals means equal within tolerances or thresholds or derivable one from the other in a known way.

BRIEF SUMMARY

According to the present invention there is provided a method of signaling between a photovoltaic module and an inverter module. The inverter module is connected to the photovoltaic module. In an initial mode of operation an initial code is modulated to produce an initial signal. The initial signal is transmitted from the inverter module to the photovoltaic module. The initial signal is received by the photovoltaic module. The operating mode is then changed to a normal mode of power conversion, and during the normal mode of operation a control signal is transmitted from the inverter to the photovoltaic module. A control code is demodulated and received from the control signal. The control code is compared with the initial code producing a comparison. The control command of the control signal is validated as a valid control command from the inverter module with the control command only acted upon when the comparison is a positive comparison. Current output of photovoltaic modules may be limited during the initial mode of operation. The initial code is typically saved in a memory. Modulating the code may be performed by varying the input impedance of the inverter module to produce a variation in voltage or current at the output of the photovoltaic module. The photovoltaic module senses the variation in voltage or current at the output of the photovoltaic module. Respective signal strengths for the initial signal and the control signal may be measured. The signal strengths are compared to produce a comparison result. When the comparison result is greater than a previously stored threshold value then an alarm is set or the control command is invalidated. Fluctuations prior to measuring the signal strength are preferably filtered out. Electrical energy is typically stored for supplying power for the varying and the sensing.

According to the present invention there is provided a photovoltaic generation system with a photovoltaic module including a first transceiver connected to the DC power line. A load module is connected to the DC power line. The load module including a second transceiver is connected to the DC power line. There is a pairing mechanism and a signaling mechanism between the first and second transceivers. Based on the pairing mechanism, another photovoltaic module or another load module in the photovoltaic generation system is excluded from signaling with either the photovoltaic module or the load module. A charge storage device may be included within the photovoltaic module adapted to store charge and supply power to the photovoltaic module. A second photovoltaic module may be attached to the photovoltaic module along with a second signaling mechanism adapted to signal between the photovoltaic module and the second photovoltaic module. The signaling mechanism is typically configured to signal controls to the second photovoltaic module by relaying commands through the second signal mechanism. The signaling mechanism may also be configured to monitor the second photovoltaic module by receiving telemetries through the second signal mechanism. A transducer is optionally connected to the DC power line and the first transceiver to modulate/demodulate a signal onto/from said power line and a sensor may be connected to the DC power line and the second transceiver to demodulate/modulate the signal from/onto said power line. In an initial mode of operation, an initial signal from the load module is transmitted to the photovoltaic module and an initial code is demodulated by the photovoltaic module. In a subsequent normal mode of operation the initial code is used to validate a control command from the load module. A memory may also be included within the photovoltaic module, the memory preferably adapted to store the initial code.

The foregoing and/or other aspects will become apparent from the following detailed description when considered in conjunction with the accompanying drawing figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is herein described, by way of example only, with reference to the accompanying drawings, wherein:

FIG. 1ashows a power generation circuit according to an embodiment of the present invention.

FIG. 1bshows further details of a transceiver attached to the output of photovoltaic modules in the power generation circuit shown inFIG. 1aaccording to an embodiment of the present invention.

FIG. 1cand1dillustrate respective methods of modulation and demodulation according to aspects of the present invention.

FIG. 1eshows further details of a control and communications unit attached to the load shown inFIG. 1a, according to features of the present invention.

FIG. 2 shows a method according to an embodiment of the present invention.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below to explain the present invention by referring to the figures.

It should be noted, that although the discussion herein relates primarily to methods in photovoltaic systems, the present invention may, by non-limiting example, alternatively be configured as well using other distributed power systems including (but not limited to) wind turbines, hydro-turbines, fuel cells, storage systems such as battery, super-conducting flywheel, and capacitors, and mechanical devices including conventional and variable speed diesel engines, Stirling engines, gas turbines, and micro-turbines.

It should be noted that although embodiments of the present invention are described in terms of an inverter as a load, the present invention may be applied equally well to other loads including non-grid tied applications such as battery chargers and DC-DC power converters.

Before explaining embodiments of the invention in detail, it is to be understood that the invention is not limited in its application to the details of design and the arrangement of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments or of being practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting.

The term “pairing or paired” as used herein refers to at least two power generation system components such as an inverter on one side, and on the other side photovoltaic panels and/or electronic modules which are “paired’ or associated with each other. “Pairing” establishes an association between an inverter and a particular set of one or more photovoltaic panels and/or electronic modules. The “pairing” between power generation components is typically performed via initial assignment of codes and storage within each power generation component. The “pairing” process may take place at the time of manufacture of power generation system components, during installation of a power generation system, during the operation of the power generation system and/or after an upgrade/modification to the power generation system. The storage of codes typically establishes the electrical connections and future communication protocols of signaling.

Referring now to the drawings, reference is now made toFIG. 1awhich shows apower generation circuit101 according to an embodiment of the present invention. Twophotovoltaic strings120, by way of example, are connected in parallel to aninverter150. Details of only one ofstrings120 are shown explicitly. In each ofstrings120, directcurrent power sources116 are serially connected. Each directcurrent power source116 includes aphotovoltaic panel100 connected to an electronic module orphotovoltaic module102. Outputs ofphotovoltaic modules102 are connected in series to formserial string120.Photovoltaic modules102 may be direct current (DC) to DC converters such as a buck circuit, boost circuit, buck/boost or buck+boost circuit or any other known switching converter topology Attached tophotovoltaic modules102 is aprocessor132 which accesses amemory130. Atransceiver108 is attached to the output ofelectronic module102 and toprocessor132. According to a feature of the present invention, one ofphotovoltaic modules102 referenced102ais a masterelectronic module102aofstring120 and controls and communicates with the other modules, i.e.slave modules102 via power line communications or wireless link.

Load150 is typically a direct current (DC) to alternating current (AC) inverter.String120 attaches across the input ofload150. The output ofload150 is typically attached to an AC grid voltage. Attached to load150 isinverter module104.Inverter module104 contains amemory module110,transceiver118 andcontrol unit112.Inverter module104 is attached to load150 withbi-directional connection114.Transducer106 is attached to the power connection to load150 and provides a signal toinverter module104.

Reference is now made toFIG. 2 which shows amethod201 according to an embodiment of the present invention.Method201 mitigates the detrimental effects of crosstalk in the communication channel along the power lines connectingphotovoltaic modules102 withinverter module104.Method201 illustrates two modes of operation, the first mode of operation is aninitial mode300 and the second mode of operation is anormal mode500 during which there is normal conversion of power.

At the beginning ofinitial mode300, current limiting (step400) typically limits the DC current output of eachelectronic module102. The limited DC current output of eachmodule102, prevents for example, the situation where theentire load150 current (I_L) is being supplied by asingle string120 or some strings are not providing any of the load current (I_L).

An initial code stored inmemory110 modulates (step202) a variation of voltage or current on the input ofload150 to produce an initial signal. The initial signal is transmitted (step203) frominverter module104. Direct electrical variation of current on the input ofload150 may be achieved by usingcontrol line114 to vary the input impedance ofload150 according to a code previously stored inmemory110. The frequency of the transmitted control signal may be between 1 Hz and 100 Hz or may also be at higher frequencies.

The initial signal transmitted (step203) frominverter module104 is then received (step205) byelectronic module102. The initial signal is sensed and a measure of the signal strength of the initial signal may be performed. The measure of the signal strength of the initial signal may be stored inmemory130. The initial signal is demodulated and/or decoded (step206) bytransceiver108 and the initial code corresponding toinverter module104 is obtained from the demodulated output voltage. The initial code corresponding toinverter module104 is stored (step207) inmemory130.

In order to end initial mode of operation indecision box209, a control signal is typically modulated (step210) and transmitted (step211) frominverter module104. The control signal is received (step213) and demodulated and/or decoded (step214) byphotovoltaic module102 and a control code is stored. Indecision box215, the control code is compared with the initial code and if the comparison is positive, i.e. the control code is the same as the initial code, thenelectronic module102 validates the command as coming frominverter module104 with whichphotovoltaic module102 is paired and not a control signal as crosstalk from another inverter module in the same photovoltaic generation field. Indecision box215, if the initial code positively compares with the control code normal conversion of power (step502) commences.

As an example, of a control signal is a keepalive signal550. When keep alive signal is encoded with a valid control code thenphotovoltaic module102 maintains normal conversion of power. Otherwise, if keepalive signal550 is not encoded with a valid control signal, such as if the signal received is “pick-up” or cross talk from another inverter in the photovoltaic field then indecision box215 keepalive signal550 is not validated andphotovoltaic module102 entersinitial mode400 which is typically a safety or current limited mode of operation until a valid keepalive signal550 signal is received to enternormal operation500.

There may be multiple possible frequencies for communication, and during pairing (initial mode300) the initial signal transmitted to and received byphotovoltaic module102 may specify tophotovoltaic module102 which frequencies to listen to and to transmit on.

Signal strength may be also be used alternatively or in addition to invalidate a control signal or at least set an alert condition. Typically, signal strength variation as measured byphotovoltaic module102 from a transmission frominverter module104 is not expected to vary more than a threshold±3 decibel (dB). A variation of signal strength more between the initial transmission (step203) and the control transmission (step211) greater than the threshold may set an alarm condition or be used alternatively or in addition to invalidate a control signal indecision box215 as being sourced by anunpaired inverter module104.

Reference is now also made toFIG. 1bwhich illustrates schematically further details ofpower source116, according to an embodiment of the present invention. The DC output ofpower source116 is connected to acharge storage device300a.Charge storage device300ahas a direct current (DC) output which supplies power to a modulator/demodulator unit302a. A transducer/sensor1106 attached to the output ofmodule102 connects to modulator/demodulator302a. Modulator/demodulator unit302ahas a bi-directional connection tomemory130 and/orprocessor132 for storing a (de)modulation voltage V_mor a code decoded from an input signal. The DC output ofcharge storage device300amay provideprocessor132 andmemory130 with DC power.Charge storage device300ais typically a battery or a capacitor which is charged via the DC output ofmodule102 during daytime operation ofpower circuit101. The charge stored instorage device300aduring daytime may be used at nighttime.

Reference is now madeFIG. 1ewhich shows further details ofinverter module104 attached to load150 inpower generation circuit101 according to an embodiment of the present invention. The output ofload150 is connected to an AC grid voltage. The AC grid voltage is connected to chargestorage device300b.Charge storage device300bis typically a battery or a capacitor which is charged via the rectified grid voltage on the output ofload150 and/or from the DC input to load150 during daytime operation.Charge storage device300bhas a direct current (DC) output which supplies power to modulator/demodulator unit302b.Transducer106, connected at the input ofload150, is connected to modulator/demodulator unit302b. Modulator/demodulator unit302balso has a connection tomemory110 orcontrol unit112.Control unit112 is attached tomemory110.Control unit112 is attached to load150 viacontrol line114. The DC output ofcharge storage device300bmay providecontrol unit112 andmemory110 with DC power.

Reference is now made toFIG. 1cwhich shows amethod103 used to operatetransceiver108/118 according to different aspects of the present invention.

The transmission of the control signal frominverter module104 is preferably performed bytransceiver118 withmethod103. The transmission of telemetries byphotovoltaic module102 is bytransceiver108 withmethod103. Whenphotovoltaic module102 sends telemetries, a source identification code identifying thephotovoltaic module102 as the source and a destination identification code identifyinginverter module104 as the destination may be included in the communication signal.

Whentransceiver108/118 is operating as a transmitter,modulator302a/302bcauses a modulated signal to be superimposed (step107) on to the DC power line.Modulator302a/302bhas an input voltage (V_m) which causes a current (I_m) to be drawn (step105) fromcharge storage device300a/300bwhich in turn draws current from the output ofmodule102 and from the input ofload150 respectively. The current drawn fromcharge storage device300a/300bis therefore a function of the input voltage i.e. modulating voltage (V_m). The superposition (step107) of the modulated signal on to the DC power line is preferably viatransducer106/1106 or by a direct electrical connection (i.e. via a coupling capacitor) to the DC power line.

According to an exemplary embodiment of the present invention, the transmission of the control signal frominverter module104 is optionally performed without the use oftransducer106. Instead the modulated control signal is made by altering of the input impedance ofload150 according to a code inmemory110 viacontrol line114. The variation of the input impedance ofload150 causes the DC input current of load150 (drawn from modules102) to vary by virtue of Ohm's law. The drawn current frommodules102 is sensed bytransducer1106 and de-modulated bytransceiver108 inmodule102.

Reference is now made toFIG. 1dwhich shows amethod109 used to operatetransceiver108/118 according to an aspect of the present invention. The reception of telemetries byinverter module104 is performed bytransceiver118 withmethod109. The reception of the control signal frominverter module104 byphotovoltaic modules102 is performed bytransceiver108 withmethod109. Whentransceiver108/118 is operating as a receiver a signal present on the DC power line is extracted (step111) from the DC power line viatransducer106/1106 or by direct electrical connection (i.e. via coupling capacitor).Demodulator302a/302bde-modulates the sensed signal present on the DC power line. In demodulation, the signal sensed and extracted (step111) from the DC power line may vary (step113) the current (I_m) drawn fromcharge storage device300a/300bwhich in turn draws current from the output ofmodule102 and from the input ofload150 respectively to produce a demodulated output voltage V_m. The demodulated output voltage (V_m) is a function of drawn current I_m.

While the invention has been described with respect to a limited number of embodiments, it will be appreciated that many variations, modifications and other applications of the invention may be made.

Claims (20)

The invention claimed is:

1. A method comprising:

receiving, by a photovoltaic module in an initial mode, an initial signal from an inverter, the initial signal having an initial code modulated therein;

receiving, by the photovoltaic module, a control signal from the inverter, the control signal having a control code modulated therein;

comparing, by the photovoltaic module, said control code with said initial code to produce a comparison;

validating, in response to the comparison being a positive comparison, a control command of said control signal as originating from the inverter; and

changing, in response to the validating of the control command, the photovoltaic module from the initial mode to a normal mode.

2. The method ofclaim 1, wherein the initial mode enables a limit on current from the photovoltaic module output to the inverter, and wherein the normal mode disables the limit on current from the photovoltaic module output to the inverter.

3. The method ofclaim 1, further comprising:

saving said initial code in a memory at the photovoltaic module.

4. The method ofclaim 1, further comprising modulating from said inverter said initial signal on a power line coupling the photovoltaic module to the inverter, wherein said modulating said initial code is performed by varying an input impedance of the inverter to produce a variation in voltage or current at an output of the photovoltaic module.

5. The method ofclaim 4, further comprising:

sensing by the photovoltaic module said variation.

6. The method ofclaim 1, wherein the receiving of the initial and control signals include sensing the initial and control signals as modulated signals superimposed on a power line coupling the photovoltaic module to the inverter; the method further comprising:

measuring respective signal strengths of said initial signal and said control signal; and

comparing said signal strengths to produce a second comparison indicating a difference in said signal strengths, wherein said validating of the control command is further in response to the difference in the signal strengths being less than a previously stored threshold value.

7. The method ofclaim 6, further comprising:

filtering out fluctuations prior to said measuring of the respective signal strengths.

8. The method ofclaim 1, further comprising:

receiving, by the photovoltaic module, a second control signal having a second control code;

comparing, by the photovoltaic module, said second control code with said initial code to produce a second comparison; and

invalidating, in response to the second comparison not being a positive comparison, a second control command of said second control signal.

9. The method ofclaim 1, further comprising:

receiving, by the photovoltaic module, a second control signal from the inverter, the second control signal having the control code modulated therein;

validating a second control command of said second control signal as originating from the inverter based on a positive comparison between the control code in the second control signal and the initial code; and

relaying, in response to the validating of the second control command, the second control command to a second photovoltaic module.

10. A photovoltaic generation system comprising:

a photovoltaic module including a first transceiver operatively connected to a DC power line; and

a load module connected to said DC power line, said load module including a second transceiver operatively connected to said DC power line, and said load module configured to transmit a pairing signal and a command signal to said first transceiver from said second transceiver;

wherein said photovoltaic module is configured to, based on said pairing signal, accept as a valid command the command signal and exclude as an invalid command a signal received by said first transceiver that is not transmitted from the load module.

11. The system ofclaim 10, further comprising:

a second photovoltaic module attached to said photovoltaic module, the second photovoltaic module having a third transceiver, wherein said photovoltaic module is configured to relay the command signal received from the load module to the second photovoltaic module by transmitting a third signal from the first transceiver to the third transceiver.

12. The system ofclaim 11, wherein said photovoltaic module is configured to receive telemetries at the first transceiver transmitted from the third transceiver of the second photovoltaic module, and transmit the telemetries from the first transceiver to the second transceiver of the load module.

13. The system ofclaim 10, further comprising:

a transducer operatively connected to said DC power line and said second transceiver to modulate the pairing and command signals onto said power line; and

a sensor operatively connected to said DC power line and said first transceiver to demodulate the pairing and command signals from said DC power line.

14. The system ofclaim 13, wherein in an initial mode of operation, the pairing signal includes an initial signal from said load module transmitted to said photovoltaic module, wherein the photovoltaic module is configured to demodulate an initial code from said initial signal, and wherein subsequently in a normal mode of operation said initial code is used by said photovoltaic module to validate the control signal from said load module.

15. The system ofclaim 14, further comprising:

a memory included within said photovoltaic module, said memory adapted to store said initial code.

16. An apparatus comprising:

a power converter configured to receive power from a photovoltaic source and provide at an output converted power to a load through a power line

a transceiver coupled to the output of the power converter; and

a processor configured to:

receive through the transceiver an initial signal superimposed on the power line from the load, the initial signal having an initial code modulated therein;

receive through the transceiver a control signal superimposed on the power line from the load, the control signal having a control code modulated therein;

compare the control code with the initial code to produce a comparison;

validate, in response to the comparison being a positive comparison, a control command in the control signal as originating from the load; and

change, in response to the validating of the control command, the photovoltaic module from operating in an initial mode to operating in a normal mode.

17. The apparatus ofclaim 16, wherein the power converter in the initial mode imposes a limit on converted power current to the load, and wherein the power converter in the normal mode disables the limit on the converted power current to the load.

18. The apparatus ofclaim 16, wherein the processor is further configured to:

measure, through the transceiver, respective signal strengths of said initial signal and said control signal; and

compare said signal strengths to produce a second comparison indicating a difference in said signal strengths, wherein the validating of the control command is further in response to the difference in said signal strengths being less than a previously stored threshold value.

19. The apparatus ofclaim 16, wherein the processor is further configured to:

receive a second control signal having a second control code;

compare the second control code with said initial code to produce a second comparison; and

invalidate, in response to the second comparison not being a positive comparison, a second control command of said second control signal.

20. The apparatus ofclaim 16, wherein the processor is further configured to:

receive a second control signal from the load, the second control signal having the control code modulated therein;

validate a second control command of said second control signal as originating from the load based on a positive comparison between the control code in the second control signal and the initial code; and

relay, in response to the validating of the second control command, the second control command to a second apparatus.

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